By virtue of their physical properties, thermoplastic polycarbonates are suitable for applications in the medical field. For these applications, it is important that the corresponding articles and moldings of the thermoplastic polycarbonates can be sterilized indefinitely without being degraded. Sterilization is carried out by irradiation with gamma-rays because treatment with steam causes permanent damage to the polycarbonates.
However, irradiation with gamma-rays also causes permanent damage to the polycarbonates by causing them to turn yellow in color. The damage caused by gamma-rays is largely suppressed by the use of aromatic sulfonic acid ester compounds in accordance with the invention.
There are various methods for making thermoplastic polycarbonates resistant to the effect of gamma-rays (see, for example, EP-A-0 296 473, U.S. Pat. No. 4,804,692 (Mo 3005) and U.S. Pat. No. 4,963,598 (Mo 3047)
It is also known that polyalkylene oxides and halogenated polycarbonates can be used in combination with one another to stabilize halogen-free polycarbonates against the effect of gamma-rays (see EPA- 0 376 289).
In addition, it is known that polyalkylene oxides can be added to spinning solutions of polycarbonates to promote their crystallization (see U.S. Pat. No. 3,385,814).
Although aromatic sulfonic acid ester compounds are not known as additives in polycarbonates, the sulfonic acid salts are known as flameproofing agents (see U.S. Pat. No. 4,880,855, U.S. Pat. No. 4,579,896, U.S. Pat. No. 4,535,108 and U.S. Pat. No. 4,001,175). Aromatic sulfonic acid salts have a weaker effect against gamma-rays than aromatic sulfonic acid ester derivatives.
The combined effect of the two components on the resistance of thermoplastic polycarbonates to the effect of gamma-rays is thus neither known nor obvious.